This invention relates generally to a process for doping a semiconductor substrate, and more specifically to a plasma enhanced diffusion process.
In the fabrication of semiconductor devices such as diodes, transistors, integrated circuits, and the like, conductivity determining impurities are introduced into localized regions of a semiconductor substrate to form PN junctions or high/low junctions. The conductivity determining dopant material can be introduced by a thermal predeposition, ion implantation, diffusion from a doped oxide, diffusion from a spin-on glass source, or the like. For many applications the various doping techniques are interchangeable, with the prime purpose of the doping technique being to introduce a prescribed amount of dopant into or onto the surface of the substrate. The dopant material can then be redistributed by thermal diffusion as required for the particular device. The combination of a predeposition of a prescribed amount of dopant and a thermal redistribution determines the junction depth and sheet resistivity of the final diffused region. Important criteria desired of any diffusion process include uniformity and reproduceability of the diffused junction, controllability of junction depth, controllability of sheet resistivity, and compatibility with a general manufacturing process. In some applications it is also important to reduce the total thermal ambient to which a device is exposed, that is, to reduce the time a device is exposed to elevated temperatures.
One process which meets most of the foregoing criteria and which is applicable in a variety of device fabrication processes is the application of a spin-on dopant material followed by thermal redistribution. Such a process is uniform and reproducible, can provide a wide range of junction depths and sheet resistivities, is highly manufacturable, and requires only a minimal amount of capital equipment. The spin-on process, however, is somewhat limited in ability to achieve shallow, low resistivity diffused regions. A need therefore existed for an improved spin-on diffusion process which could achieve more heavily doped diffused regions.
It is therefore an object of this invention to provide an improved spin-on diffusion method.
It is another object of this invention to provide an improved spin-on diffusion method capable of achieving low resistivity diffused regions.
It is yet another object of this invention to provide an improved spin-on diffusion process which involves less thermal ambient than other diffusion processes for the same diffusion results.